The present invention relates to a volume flow control for hydraulic systems of vehicles, especially for steering devices of motor vehicles, having a pump supplying a main consuming device and at least one auxiliary device with a hydraulic medium that flows via a main connection to the main consuming device and via an auxiliary connection through a valve having at least one throttle to the auxiliary device. The auxiliary connection is pressurized by a main piston.
In such known devices a stationary orifice is provided within a valve housing in front of a main piston through which the auxiliary volume flow in direction to the auxiliary consuming device is branched off from the main volume flow. When the auxiliary consuming device is turned on, the branched-off auxiliary volume flow is returned to the main piston which is thus displaced in the direction toward the stationary orifice and thus pressurizes the hydraulic medium that is located between the orifice and the main piston. Depending on the magnitude of the pressure a varying amount of hydraulic medium flows through the throttle location of the orifice to the auxiliary consuming device. The throttle cross-section is large in order to ensure that a sufficiently high pressure and a sufficiently high amount of hydraulic medium can reach the auxiliary consuming device when the main consuming device operates at a low operational pressure. This results in that for a higher operating pressure the amount of hydraulic medium flowing to the auxiliary consuming device is also correspondingly higher so that for the main consuming device only a respectively reduced amount of hydraulic medium is available. This may result in a reduced operability of the main consuming device. For example, when the main consuming device is the steering device of a motor vehicle, the steering velocity four a respectively reduced amount of hydraulic medium is thus reduced.
It is therefore an object of the present invention to improve the volume flow control of the aforementioned kind such that independent of the operational pressure at the main consuming device the required amount of hydraulic medium can always be supplied to the auxiliary consuming device.